Reaction kinetics of the solid state polymerization of poly(bisphenol A carbonate)

The kinetics of solid-state polymerization (SSP) of poly(bisphenol A carbonate) was investigated with N₂ as the sweep gas. The N₂ flow rate and prepolymer particle size were chosen to eliminate the influence of both external and internal phenol diffusion, and to ensure that the kinetics was controlled by the rate of the forward transesterification reaction. The forward reaction rate constants were evaluated at different temperatures between 120 and 165 °C, and the activation energy for SSP of poly(bisphenol A carbonate) with N₂ as the sweep gas was determined to be 99.6 kJ/mol. At each temperature, the polymer molecular weight increased with time, eventually reaching an asymptotic value. The asymptotic molecular weight increased with temperature. The glass transition temperature (T_g) of the polymer increased as the molecular weight increased. At lower reaction temperatures, T_g approaches the reaction temperature as the polymerization proceeds, and the achievable molecular weight appears to be limited by decreased end group mobility. At the highest reaction temperature, which was well above the final T_g of the polymer, the stoichiometric ratio of the two end groups appears to determine the achievable molecular weight.